Physicians have long sought better methods of judging proper therapeutic dosages and diagnosing digitalis toxicity. Recently, Smith, Bulter and Haber in an article entitled "Determination of Therapeutic and Toxic Serum Digoxin Concentrations by Radioimmunoassay", New England Journal of Medicine, Vol. 281, Pages 1212-1216 (1969) disclosed a method for determining serum digoxin concentrations by the use of tritiated digoxin, but the use of tritiated digoxin in the detection of serum digoxin of nonogram levels is subject to the inherent disadvantages of liquid scintillation counting which, in conjunction with the relatively low specific activity of commercially available tritiated digoxin, necessitates relatively large sample volumes and/or increased counting times in order to attain the requisite sensitivity and accuracy.
As a result of the limitations of tritiated cardenolide glycosides for radioimmunological assay, there is a need for other radiolabeled compounds, which can be effectively employed in the radioimmunological assay of digoxin in human serum.